Five-year results of a randomized controlled clinical trial comparing zirconia and titanium abutments supporting single-implant crowns in canine and posterior regions

OBJECTIVES: To test the survival rates, and the technical and biological complication rates of customized zirconia and titanium abutments 5 years after crown insertion. MATERIAL AND METHODS: Twenty-two patients with 40 single implants in maxillary and mandibular canine and posterior regions were included. The implant sites were randomly assigned to zirconia abutments supporting all-ceramic crowns or titanium abutments supporting metal-ceramic crowns. Clinical examinations were performed at baseline, and at 6, 12, 36 and 60 months of follow-up. The abutments and reconstructions were examined for technical and/or biological complications. Probing pocket depth (PPD), plaque control record (PCR) and Bleeding on Probing (BOP) were assessed at abutments (test) and analogous contralateral teeth (control). Radiographs of the implants revealed the bone level (BL) on mesial (mBL) and distal sides (dBL). Data were statistically analyzed with nonparametric mixed models provided by Brunner and Langer and STATA (P < 0.05). RESULTS: Eighteen patients with 18 zirconia and 10 titanium abutments were available at a mean follow-up of 5.6 years (range 4.5-6.3 years). No abutment fracture or loss of a reconstruction occurred. Hence, the survival rate was 100% for both. Survival of implants supporting zirconia abutments was 88.9% and 90% for implants supporting titanium abutments. Chipping of the veneering ceramic occurred at three metal-ceramic crowns supported by titanium abutments. No significant differences were found at the zirconia and titanium abutments for PPD (meanPPD(ZrO2) 3.3 ± 0.6 mm, mPPD(T) (i) 3.6 ± 1.1 mm), PCR (mPCR(Z) (rO) (2) 0.1 ± 0.3, mPCR(T) (i) 0.3 ± 0.2) and BOP (mBOP(Z) (rO) (2) 0.5 ± 0.3, mBOP(T) (i) 0.6 ± 0.3). Moreover, the BL was similar at implants supporting zirconia and titanium abutments (mBL(Z) (rO) (2) 1.8 ± 0.5, dBL(Z) (rO) (2) 2.0 ± 0.8; mBL(T) (i) 2.0 ± 0.8, dBL(T) (i) 1.9 ± 0.8). CONCLUSIONS: There were no statistically or clinically relevant differences between the 5-year survival rates, and the technical and biological complication rates of zirconia and titanium abutments in posterior regions.

Osseointegration and biocompatibility of different metal implants-a comparative experimental investigation in sheep

Background In the present study, 4 different metallic implant materials, either partly coated or polished, were tested for their osseointegration and biocompatibility in a pelvic implantation model in sheep. Methods Materials to be evaluated were: Cobalt-Chrome (CC), Cobalt-Chrome/Titanium coating (CCTC), Cobalt-Chrome/Zirconium/Titanium coating (CCZTC), Pure Titanium Standard (PTST), Steel, TAN Standard (TANST) and TAN new finish (TANNEW). Surgery was performed on 7 sheep, with 18 implants per sheep, for a total of 63 implants. After 8 weeks, the specimens were harvested and evaluated macroscopically, radiologically, biomechanically (removal torque), histomorphometrically and histologically. Results Cobalt-Chrome screws showed significantly (p = 0.031) lower removal torque values than pure titanium screws and also a tendency towards lower values compared to the other materials, except for steel. Steel screws showed no significant differences, in comparison to cobalt-chrome and TANST, however also a trend towards lower torque values than the remaining materials. The results of the fluorescence sections agreed with those of the biomechanical test. Histomorphometrically, there were no significant differences of bone area between the groups. The BIC (bone-to-implant-contact), used for the assessment of the osseointegration, was significantly lower for cobalt-chrome, compared to steel (p = 0.001). Steel again showed a lower ratio (p = 0.0001) compared to the other materials. Conclusion This study demonstrated that cobalt-chrome and steel show less osseointegration than the other metals and metal-alloys. However, osseointegration of cobalt-chrome was improved by zirconium and/or titanium based coatings (CCTC, TANST, TAN, TANNEW) being similar as pure titanium in their osseointegrative behavior.

Population-based design of mandibular fixation plates with bone quality and morphology considerations

In this paper we present a new population-based implant design methodology, which advances the state-of-the-art approaches by combining shape and bone quality information into the design strategy. The method may enhance the mechanical stability of the fixation and reduces the intra-operative in-plane bending which might impede the functionality of the locking mechanism. The computational method is presented for the case of mandibular locking fixation plates, where the mandibular angle and the bone quality at screw locations are taken into account. The method automatically derives the mandibular angle and the bone thickness and intensity values at the path of every screw from a set of computed tomography images. An optimization strategy is then used to optimize the two parameters of plate angle and screw position. The method was applied to two populations of different genders. Results for the new design are presented along with a comparison with a commercially available mandibular locking fixation plate (MODUS(®) TriLock(®) 2.0/2.3/2.5, Medartis AG, Basel, Switzerland). The proposed designs resulted in a statistically significant improvement in the available bone thickness when compared to the standard plate. There is a higher probability that the proposed implants cover areas of thicker cortical bone without compromising the bone mineral density around the screws. The obtained results allowed us to conclude that an angle and screw separation of 129° and 9 mm for females and 121° and 10 mm for males are more suitable designs than the commercially available 120° and 9 mm.

Correlation of Pullout Force of Kirschner (K-) Wire to Other Factors Indicative of Bone Quality

More than 250,000 hip fractures occur annually in the United States and the most common fracture location is the femoral neck, the weakest region of the femur. Hip fixation surgery is conducted to repair hip fractures by using a Kirschner (K-) wire as a temporary guide for permanent bone screws. Variation has been observed in the force required to extract the K-wire from the femoral head during surgery. It is hypothesized that a relationship exists between the K-wire pullout force and the bone quality at the site of extraction. Currently, bone mineral density (BMD) is used as a predictor for bone quality and strength. However, BMD characterizes the entire skeletal system and does not account for localized bone quality and factors such as lifestyle, nutrition, and drug use. A patient’s BMD may not accurately describe the quality of bone at the site of fracture. This study aims to investigate a correlation between the force required to extract a K-wire from femoral head specimens and the quality of bone. A procedure to measure K-wire pullout force was developed and tested with pig femoral head specimens. The procedure was implemented on 8 human osteoarthritic femoral head specimens and the average pullout force for each ranged from 563.32 ± 240.38 N to 1041.01 ± 346.84 N. The data exhibited significant variation within and between each specimen and no statistically significant relationships were determined between pullout force and patient age, weight, height, BMI, inorganic to organic matter ratio, and BMD. A new testing fixture was designed and manufactured to merge the clinical and research environments by enabling the physician to extract the K-wire from each bone specimen himself. The new device allows the physician to gather tactile feedback on the relative ease of extraction while load history is recorded similar to the previous procedure for data acquisition. Future work will include testing human bones with the new device to further investigate correlations for predicting bone quality.

Trochanteric flip osteotomy for cranial extension and muscle protection in acetabular fracture fixation using a Kocher-Langenbeck approach

OBJECTIVE: To describe the advantages and surgical technique of a trochanteric flip osteotomy in combination with a Kocher-Langenbeck approach for the treatment of selected acetabular fractures. DESIGN: Consecutive series, teaching hospital. METHODS: Through mobilization of the vastus lateralis muscle, a slice of the greater trochanter with the attached gluteus medius muscle can be flipped anteriorly. The gluteus minimus muscle can then be easily mobilized, giving free access to the posterosuperior and superior acetabular wall area. Damage to the abductor muscles by vigorous retraction can be avoided, potentially resulting in less ectopic ossification. Ten consecutive cases of acetabular fractures treated with this approach are reported. In eight cases, an anatomic reduction was achieved; in the remaining two cases with severe comminution, the reduction was within one to three millimeters. The trochanteric fragment was fixed with two 3.5-millimeter cortical screws. RESULTS: All osteotomies healed in anatomic position within six to eight weeks postoperatively. Abductor strength was symmetric in eight patients and mildly reduced in two patients. Heterotopic ossification was limited to Brooker classes 1 and 2 without functional impairment at an average follow-up of twenty months. No femoral head necrosis was observed. CONCLUSION: This technique allows better visualization, more accurate reduction, and easier fixation of cranial acetabular fragments. Cranial migration of the greater trochanter after fixation with two screws is unlikely to occur because of the distal pull of the vastus lateralis muscle, balancing the cranial pull of the gluteus medius muscle.

Horizontal ridge augmentation using autogenous block grafts and the guided bone regeneration technique with collagen membranes: a clinical study with 42 patients

OBJECTIVE: To analyze the clinical outcome of horizontal ridge augmentation using autogenous block grafts covered with an organic bovine bone mineral (ABBM) and a bioabsorbable collagen membrane. MATERIAL AND METHODS: In 42 patients with severe horizontal bone atrophy, a staged approach was chosen for implant placement following horizontal ridge augmentation. A block graft was harvested from the symphysis or retromolar area, and secured to the recipient site with fixation screws. The width of the ridge was measured before and after horizontal ridge augmentation. The block graft was subsequently covered with ABBM and a collagen membrane. Following a tension-free primary wound closure and a mean healing period of 5.8 months, the sites were re-entered, and the crest width was re-assessed prior to implant placement. RESULTS: Fifty-eight sites were augmented, including 41 sites located in the anterior maxilla. The mean initial crest width measured 3.06 mm. At re-entry, the mean width of the ridge was 7.66 mm, with a calculated mean gain of horizontal bone thickness of 4.6 mm (range 2-7 mm). Only minor surface resorption of 0.36 mm was observed from augmentation to re-entry. CONCLUSIONS: The presented technique of ridge augmentation using autogenous block grafts with ABBM filler and collagen membrane coverage demonstrated successful horizontal ridge augmentation with high predictability. The surgical method has been further simplified by using a resorbable membrane. The hydrophilic membrane was easy to apply, and did not cause wound infection in the rare instance of membrane exposure.

Short anterior correction of the thoracolumbar/lumbar curve in King 1 idiopathic scoliosis: the behaviour of the instrumented and non-instrumented curves and the trunk balance

This is a retrospective clinical, radiological and patient outcome assessment of 21 consecutive patients with King 1 idiopathic adolescent scoliosis treated by short anterior selective fusion of the major thoracolumbar/lumbar (TL/L) curve. Three-dimensional changes of both curves, changes in trunk balance and rib hump were evaluated. The minimal follow-up was 24 months (max. 83). The Cobb angle of the TL/L curve was 52 degrees (45-67 degrees) with a flexibility of 72% (40-100%). The average length of the main curve was 5 (3-8) segments. An average of 3 (2-4) segments was fused using rigid single rod implants with side-loading screws. The Cobb angle of the thoracic curve was 33 degrees (18-50 degrees) with a flexibility of 69% (29-100%). The thoracic curve in bending was less than 20 degrees in 17 patients, and 20-25 degrees in 4 patients. In the TL/L curve there was an improvement of the Cobb angle of 67%, of the apex vertebral rotation of 51% and of the apex vertebral translation of 74%. The Cobb angle of the thoracic curve improved 29% spontaneously. Shoulder balance improved significantly from an average preoperative imbalance of 14.5-3.1 mm at the last follow-up. Seventy-five percent of the patients with preoperative positive shoulder imbalance (higher on the side of the thoracic curve) had levelled shoulders at the last follow-up. C7 offset improved from a preoperative 19.8 (0-40) to 4.8 (0-18) mm at the last follow-up. There were no significant changes in rotation, translation of the thoracic curve and the clinical rib hump. There were no significant changes in thoracic kyphosis or lumbar lordosis. The average score of the SRS-24 questionnaire at the last follow-up was 91 points (max. 120). We conclude that short anterior selective fusion of the TL/L curve in King 1 scoliosis with a thoracic curve bending to 25 degrees or less (Type 5 according to Lenke classification) results in a satisfactory correction and a balanced spine. Short fusions leave enough mobile lumbar segments for the establishment of global spinal balance. A positive shoulder imbalance is not a contraindication for this procedure. Structural interbody grafts are not necessary to maintain lumbar lordosis.

Harvesting local cylinder autograft from adjacent vertebral body for anterior lumbar interbody fusion: surgical technique, operative feasibility and preliminary clinical results

Autogenous iliac crest has long served as the gold standard for anterior lumbar arthrodesis although added morbidity results from the bone graft harvest. Therefore, femoral ring allograft, or cages, have been used to decrease the morbidity of iliac crest bone harvesting. More recently, an experimental study in the animal showed that harvesting local bone from the anterior vertebral body and replacing the void by a radio-opaque beta-tricalcium phosphate plug was a valid concept. However, such a concept precludes theoretically the use of posterior pedicle screw fixation. At one institution a consecutive series of 21 patients underwent single- or multiple-level circumferential lumbar fusion with anterior cages and posterior pedicle screws. All cages were filled with cancellous bone harvested from the adjacent vertebral body, and the vertebral body defect was filled with a beta-tricalcium phosphate plug. The indications for surgery were failed conservative treatment of a lumbar degenerative disc disease or spondylolisthesis. The purpose of this study, therefore, was to report on the surgical technique, operative feasibility, safety, benefits, and drawbacks of this technique with our primary clinical experience. An independent researcher reviewed all data that had been collected prospectively from the onset of the study. The average age of the patients was 39.9 (26-57) years. Bone grafts were successfully harvested from 28 vertebral bodies in all but one patient whose anterior procedure was aborted due to difficulty in freeing the left common iliac vein. This case was converted to a transforaminal interbody fusion (TLIF). There was no major vascular injury. Blood loss of the anterior procedure averaged 250 ml (50-350 ml). One tricalcium phosphate bone plug was broken during its insertion, and one endplate was broken because of wrong surgical technique, which did not affect the final outcome. One patient had a right lumbar plexopathy that was not related to this special technique. There was no retrograde ejaculation, infection or pseudoarthrosis. One patient experienced a deep venous thrombosis. At the last follow up (mean 28 months) all patients had a solid lumbar spine fusion. At the 6-month follow up, the pain as assessed on the visual analog scale (VAS) decreased from 6.9 to 4.5 (33% decrease), and the Oswestry disability index (ODI) reduced from 48.0 to 31.7 with a 34% reduction. However, at 2 years follow up there was a trend for increase in the ODI (35) and VAS (5). The data in this study suggest that harvesting a cylinder of autograft from the adjacent vertebral body is safe and efficient. Filling of the void defect with a beta-tricalcium phosphate plug does not preclude the use of posterior pedicle screw stabilization.

Validity and clinical significance of biomechanical testing of implant/bone interface

Purpose: The aim of this paper was to review the clinical literature on the Resonance frequency analysis (RFA) and Periotest techniques in order to assess the validity and prognostic value of each technique to detect implants at risk for failure. Material and methods: A search was made using the PubMed database to find clinical studies using the RFA and/or Periotest techniques. Results: A limited number of clinical reports were found. No randomized-controlled clinical trials or prospective cohort studies could be found for validity testing of the techniques. Consequently, only a narrative review was prepared to cover general aspects of the techniques, factors influencing measurements and the clinical relevance of the techniques. Conclusions: Factors such as bone density, upper or lower jaw, abutment length and supracrestal implant length seem to influence both RFA and Periotest measurements. Data suggest that high RFA and low Periotest values indicate successfully integrated implants and that low/decreasing RFA and high/increasing Periotest values may be signs of ongoing disintegration and/or marginal bone loss. However, single readings using any of the techniques are of limited clinical value. The prognostic value of the RFA and Periotest techniques in predicting loss of implant stability has yet to be established in prospective clinical studies. To cite this article: Aparicio C, Lang N P, Rangert B. Validity and clinical significance of biomechanical testing of implant/bone interface. Clin. Oral Imp. Res., 17 (Suppl. 2), 2006; 2-7.

Significance of primary stability for osseointegration of dental implants

AIM: To investigate the significance of the initial stability of dental implants for the establishment of osseointegration in an experimental capsule model for bone augmentation. MATERIAL AND METHODS: Sixteen male rats were used in the study. In each rat, muscle-periosteal flaps were elevated on the lateral aspect of the mandibular ramus on both sides, resulting in exposure of the bone surface. Small perforations were then produced in the ramus. A rigid, hemispherical Teflon capsule with a diameter of 6 mm and a height of 4 mm and with a hole in its middle portion, prepared to fit the circumference of an ITI HC titanium implant of 2.8 mm in diameter, was fixed to the ramus using 4 mini-screws. On one side of the jaw, the implant was placed through the hole in such a way that its apex did not make contact with the mandibular ramus (test). This placement of the implant did not ensure primary stability. On the other side of the jaw, a similar implant was placed through the hole of the capsule in such a way that contact was made between the implant and the surface of the ramus (control). This provided primary stability of the implant. After placement of the implants, the soft tissues were repositioned over the capsules and sutured. After 1, 3, 6 and 9 months, four animals were sacrificed and subjected to histometric analysis. RESULTS: The mean height of direct bone-to-implant contact of implants with primary stability was 38.8%, 52.9%, 64.6% and 81.3% of the implant length at 1, 3, 6 and 9 months, respectively. Of the bone adjacent to the implant surface, 28.1%, 28.9%, 52.6% and 69.6%, respectively, consisted of mineralized bone. At the test implants, no bone-to-implant contact was observed at any observation time or in any of these non-stabilized specimens. CONCLUSION: The findings of the present study indicate that primary implant stability is a prerequisite for successful osseointegration, and that implant instability results in fibrous encapsulation, thus confirming previously made clinical observations.

A systematic review of the 5-year survival and complication rates of implant-supported single crowns

OBJECTIVES: The objective of this systematic review was to assess the 5-year survival of implant-supported single crowns (SCs) and to describe the incidence of biological and technical complications. METHODS: An electronic MEDLINE search complemented by manual searching was conducted to identify prospective and retrospective cohort studies on SCs with a mean follow-up time of at least 5 years. Failure and complication rates were analyzed using random-effects Poisson's regression models to obtain summary estimates of 5-year proportions. RESULTS: Twenty-six studies from an initial yield of 3601 titles were finally selected and data were extracted. In a meta-analysis of these studies, survival of implants supporting SCs was 96.8% [95% confidence interval (CI): 95.9-97.6%] after 5 years. The survival rate of SCs supported by implants was 94.5% (95% CI: 92.5-95.9%) after 5 years of function. The survival rate of metal-ceramic crowns, 95.4% (95% CI: 93.6-96.7%), was significantly (P=0.005) higher than the survival rate, 91.2% (95% CI: 86.8-94.2%), of all-ceramic crowns. Peri-implantitis and soft tissue complications occurred adjacent to 9.7% of the SCs and 6.3% of the implants had bone loss exceeding 2 mm over the 5-year observation period. The cumulative incidence of implant fractures after 5 years was 0.14%. After 5 years, the cumulative incidence of screw or abutment loosening was 12.7% and 0.35% for screw or abutment fracture. For supra-structure-related complications, the cumulative incidence of ceramic or veneer fractures was 4.5%. CONCLUSION: It can be concluded that after an observation period of 5 years, high survival rates for implants and implant-supported SCs can be expected. However, biological and particularly technical complications are frequent.

Clinical field trial examining an implant with a sand-blasted, acid-etched surface

BACKGROUND: Conventionally, endosseous dental implants have required 3 to 6 months of uninterrupted healing based on observations for dental implants that were characterized by a relatively smooth machined surface. Many studies have since demonstrated that implants with a roughened surface resulted in greater bone apposition, earlier bone contact, and a stronger bond between the implant and the bone, suggesting that implants with roughened surfaces could be loaded earlier than 3 to 6 months. Formal clinical studies confirmed that implants with rough surfaces can have abutments placed and be loaded occlusally as early as 6 weeks postplacement. The purpose of this prospective, human clinical investigation was to evaluate a large number of implants with a specific rough surface (sand-blasted acid-etched [SLA]) placed in everyday practice under routine private-practice conditions. METHODS: A prospective, multicenter, human clinical observational study was initiated with the goal of recruiting a minimum of 500 patients and 800 implants. The implants were to be placed and restored in predominantly private-practice settings around the world. Ninety-two practitioners in 16 countries agreed to participate, and 86 followed the study design. Patients had to be in good health, have sufficient bone to encase the implant, and agree to return for recall appointments. Exclusion criteria included heavy smoking (>10 cigarettes a day) and bone augmentation procedures at the implant site. All implants were two-piece (an abutment was to be placed after 6 weeks of healing) and were characterized by the presence of a transmucosal polished collar. Each implant had an SLA surface. All implants were positioned using a non-submerged (single-stage) surgical technique. Survival and success rates were calculated by life-table analyses. RESULTS: A total of 706 patients were enrolled and 1,406 implants were placed. In the final analyses, 590 patients with 990 implants (70.4% of those enrolled) met all inclusion criteria, including placement of an abutment and provisional restoration within 63 days of surgical placement. The majority of implants were 10 and 12 mm long (78.7%) and were placed in type II and III bone (87%). Seventy-three percent of the implants were placed in the mandible, and 27% were placed in the maxilla. The cumulative survival rate was 99.56% at 3 years and 99.26% at 5 years. The overall success rate was 99.12% at 3 years and 97.38% after 5 years. CONCLUSIONS: Under private-practice conditions, implants with an SLA surface could be placed and restored predictably within 6 to 8 weeks. Data from this prospective, multicenter, human observational study reinforced the results of more formal clinical studies and demonstrated that implants with the SLA surface can be restored in patients in approximately half of the time of conventional healing periods.

[Irritation of the iliopsoas tendon after total hip arthroplasty]

Chronic irritation of the iliopsoas tendon is a rare cause of persistent pain after total joint replacement of the hip. In the majority of cases, pain results from a mechanical conflict between the iliopsoas tendon and the anterior edge of the acetabular cup after total hip arthroplasty. Pain can be reproduced by active flexion of the hip and by active raising of the straightened leg. In addition, painful leg raising against resistance and passive hyperextension are suggestive of an irritation of the iliopsoas tendon. Symptoms evolve from a mechanical irritation of the iliopsoas tendon and an oversized or retroverted acetabular cup, screws penetrating into the inner aspect of the ilium, or from bone cement protruding beyond the anterior acetabular rim. The diagnosis may be assumed on conventional radiographs and confirmed by CT scans. Fifteen patients with psoas irritation after total hip replacement are reported on. Eleven patients were treated surgically. The acetabular cup was revised and reoriented with more anteversion in six patients, isolated screws penetrating into the tendon were cut and leveled in three patients, and prominent bone cement in conflict with the tendon was resected once. A partial release of the iliopsoas tendon only was performed in another patient. Follow-up examination (range: 11-89 months) revealed that nine patients were free of pain and two patient had mild residual complaints. Psoas irritation in combination with total hip replacement can be prevented by a correct surgical technique, especially with proper selection of the cup size and insertion of the acetabular cup avoiding a rim position exceeding the level of the anterior acetabular rim.

Zirconia for teeth and implants

This case series reports on the use of nonsilica-based high-strength full ceramics for different prosthetic indications. Fifty-two consecutive patients received tooth- or implant-supported zirconia reconstructions during a 2-year period. The observation period for reexamination was 12 to 30 months. The most frequent indications were single crowns and short-span fixed partial dentures. A few implant superstructures were screw-retained, whereas all remaining restorations were cemented on natural teeth or zirconia implant abutments. Clinical examination included biologic (probing depths, bleeding on probing) and esthetic (Papilla Index) parameters, as well as technical complications. No implant was lost or caused any problems, but two teeth were lost after horizontal fracture. Overall, the periodontal parameters were favorable. Fractures of frameworks or implant abutments were not observed. Abutment-screw loosening occurred once for one premolar single crown. Furthermore, five implant crowns in the posterior region exhibited chipping of the porcelain veneering material. With regard to esthetics, no reconstructions were considered unacceptable, but three crowns were remade shortly after delivery. In this short-term study, it was observed that biologic, esthetic, and mechanical properties of zirconia were favorable, and the material could be used in various prosthetic indications on teeth or implants.

Within-subject comparison of two rigid bar designs connecting two interforaminal implants: patients' satisfaction and prosthetic results

BACKGROUND: There is evidence for the superiority of two-implant overdentures over complete dentures in the mandible. Various anchorage devices were used to provide stability to overdentures. The aim of the present study was to compare two designs of a rigid bar connecting two mandibular implants. MATERIALS AND METHODS: Completely edentulous patients received a new denture in the maxilla and an implant-supported overdenture in the mandible. They were randomly allocated to two groups (A or B) with regard to the bar design. A standard U-shaped bar (Dolder bar) was used connecting the two implants in a straight line. For comparison, precision attachments were soldered distal to the bar copings. Group A started the study with the standard bar (S-bar), while group B started with the attachment-bar (A-bar). After 3 months, they had to answer a questionnaire (visual analogue scale [VAS]); then the bar design was changed in both groups. After a period of another 3 months, the patients had to answer the same questions; then they had the choice to keep their preferred bar. Now the study period was extended to another year of observation, and the patients answered again the same questionnaire. In vivo force measurements were carried out with both bar types at the end of the test periods. The prosthetic maintenance service carried out during the 6-month period was recorded for both bar types in both groups. Statistical analysis as performed with the SPSS statistical package (SPSS Inc., Chicago, IL, USA). RESULTS: Satisfaction was high in both groups. Group B, who had entered the study with the attachment bar, gave slightly better ratings to this type for four items, while in group A, no differences were found. At the end of the 6-month comparison period, all but one patient wished to continue to wear the attachment bar. Prosthetic service was equal in groups A and B, but the total number of interventions is significantly higher in the attachment bar. Force patterns of maximum biting were similar in both bar designs, but exhibited significantly higher axial forces in the attachment bar. CONCLUSIONS: Both bar designs provide good retention and functional comfort. High stability appears to be an important factor for the patients' satisfaction and oral comfort. Rigid retention results in a higher force impact and appears to evoke the need for the retightening of occlusal screws, resulting in more maintenance service.